“Half moon” gap on head - what’s it for?

[Dakota]

I have a 340 with stock heads and intake manifold.  While chasing a small oil leak from under the Mopar Performance valve cover on the driver side, I came across the "half moon" gap in the head in line with the carb flange.  It's not covered by the intake manifold gasket. 

Assuming (maybe incorrectly) that the guy who built my engine did it correctly, I'm left wondering why this gap exists?   

If this is part of the heat riser system it would explain why the paint on the intake manifold is getting charred. 

[Cudajason]

it is there to collect dropped screws and accelerator pump cams from Holey carbs. 

it is assembled correctly.

[Chryco Psycho]

Yes it collects parts , the heat riser passage is in the middle & it is an air gap to keep the heads cooler , I always block that port as most of these cars are not driven n cold weather anymore .